The authors proposed to study three lesions in germ-free (G-F) animals: burns, encephalopathy following portacaval shunt and stress ulcer. Animals will be burned and eschar separation in G-F animals will be investigated. Metabolic rate and oxygen utilization will be compared in G-F and conventional animals following burn injury. Stress ulcer will be induced in rats and examined by ultra microscopy. The effect of a variety of bacterial flora will be compared in Gnotobiotic animals. Hepatic encephalopathy will be induced by performing portacaval shunts in G-F and conventional dogs and rats. The effect of various dietary substrates will be compared following shunts.